The present invention generally relates to propulsion systems and more specifically to gas generator design and assembly for the catalytic decomposition of high concentration hydrogen peroxide and the catalytic combustion of hydrocarbon/air mixtures.
Safer, less toxic propellants that meet operational performance requirements have long been sought by the propulsion industry. The commitment to increasingly safer and lower cost orbit space operations, as evidenced by a central charter of the Space Launch Initiative, has made success in testing less toxic propellants more imperative than ever. Less toxic propulsion systems are being developed to replace engine systems that use more hazardous propellants, such as Nitrogen Tetroxide (NTO) and Monomethyl Hydrazine (MMH).
Hydrogen peroxide offers many potential benefits as a non-toxic propellant source for target, space, and on-orbit applications. Hydrogen peroxide can be decomposed by passing it over a catalyst. The catalyst bed decomposes the hydrogen peroxide to produce super-heated steam and oxygen. The hot gases can be used to drive gas turbines, provide thrust as a monopropellant, provide an oxidizer for bi-propellant systems, or function as an igniter for a rocket engine when combined with fuels like kerosene.
Ninety-eight (98%) percent hydrogen peroxide is an excellent oxidizer for many space applications, both in monopropellant and bipropellant systems, because it is non-cryogenic, has high density, and can be used as a regenerative coolant. However, the high adiabatic decomposition temperature of 98% hydrogen peroxide (1734 degrees Fahrenheit at one atmosphere, versus 1364 degrees Fahrenheit for 90% hydrogen peroxide) and the increase in volume due the temperature increase and phase change from a liquid to a gas creates difficulties in making a practical gas generator using this propellant.
In the past, hydrogen peroxide catalyst beds have been plagued with performance problems such as decomposition pressure instabilities, shorter-than predicted life, delayed starts, and low c* (catalytic decomposition) efficiency. Even the best catalyst, if not packed into a proper configuration, will have poor performance. The catalyst screens must be configured into a packed catalyst bed in a very-specific manner in order to yield smooth decomposition, long life, quick starts (without pre-heat), and high decomposition efficiency. There are many variables, including fluid distribution plate design, bed dimensions, screen type, screen positioning, number of screens, assembly sequence, and pack pressure that have a profound effect on performance.
Typical gas generators for high concentration hydrogen peroxide are prone to pressure oscillations associated with the decomposition process. The pressure oscillations tend to manifest within the catalyst bed and can be amplified by the inherent design and installation of the gas generator within a system.
Therefore, there is a need for a gas generator incorporating a high temperature catalyst system in a design which significantly mitigates the pressure oscillations of the decomposition process of high concentration hydrogen peroxide.
Further, a similar need exists for gas generator that may be used for the catalytic combustion of hydrocarbon/air mixtures. Such a catalyst system could be used in the power generation or automotive industries for emission control applications.
The present invention proposes a design and an assembly method for a high performance catalyst bed gas generator. The catalyst bed within the gas generator decomposes high temperature propellants and consists of multiple screen sections contained between an injector plate and an aft distribution plate within a cartridge housing. The multiple screen sections include a diffuser screen section, an initiator screen section, an active screen section having either a Type I or Type II mixed metal oxide (MMO) catalyst composition, and preferably a thermal screen section. The catalyst bed design is suitable for efficiently and reliably decomposing up to about 99% hydrogen peroxide propellants and withstanding the hot gas environment for durations in excess of 10,000 seconds.
The axial flow packed catalyst bed of the present invention exhibits smooth decomposition, long life, quick starts (without pre-heat), and high c* (catalytic decomposition) efficiency.
The design and assembly of the present invention is also available for other propellant systems that involve similar decomposition processes. For example, the Type II catalyst systems described above may also be used in propellant systems involving the decomposition of methane or other gaseous materials.
Other objects and advantages of the present invention will become apparent upon considering the following detailed description and appended claims, and upon reference to the accompanying drawings.